/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.search.function;

import org.apache.lucene.index.IndexReader;
import org.apache.solr.search.function.DocValues;
import org.apache.solr.search.function.ValueSource;
import org.apache.lucene.search.FieldCache;

import java.io.IOException;
import java.util.Map;

/**
 * Obtains the ordinal of the field value from the default Lucene
 * {@link org.apache.lucene.search.FieldCache} using getStringIndex() and
 * reverses the order. <br>
 * The native lucene index order is used to assign an ordinal value for each
 * field value. <br>
 * Field values (terms) are lexicographically ordered by unicode value, and
 * numbered starting at 1. <br>
 * Example of reverse ordinal (rord):<br>
 * If there were only three field values: "apple","banana","pear" <br>
 * then rord("apple")=3, rord("banana")=2, ord("pear")=1
 * <p>
 * WARNING: ord() depends on the position in an index and can thus change when
 * other documents are inserted or deleted, or if a MultiSearcher is used. <br>
 * WARNING: as of Solr 1.4, ord() and rord() can cause excess memory use since
 * they must use a FieldCache entry at the top level reader, while sorting and
 * function queries now use entries at the segment level. Hence sorting or using
 * a different function query, in addition to ord()/rord() will double memory
 * use.
 * 
 * @version $Id: ReverseOrdFieldSource.java 1065312 2011-01-30 16:08:25Z rmuir $
 */

public class ReverseOrdFieldSource extends ValueSource {
	public String field;

	public ReverseOrdFieldSource(String field) {
		this.field = field;
	}

	@Override
	public String description() {
		return "rord(" + field + ')';
	}

	@Override
	public DocValues getValues(Map context, IndexReader reader)
			throws IOException {
		final FieldCache.StringIndex sindex = FieldCache.DEFAULT
				.getStringIndex(reader, field);

		final int arr[] = sindex.order;
		final int end = sindex.lookup.length;

		return new DocValues() {
			@Override
			public float floatVal(int doc) {
				return (float) (end - arr[doc]);
			}

			@Override
			public int intVal(int doc) {
				return (end - arr[doc]);
			}

			@Override
			public long longVal(int doc) {
				return (long) (end - arr[doc]);
			}

			@Override
			public double doubleVal(int doc) {
				return (double) (end - arr[doc]);
			}

			@Override
			public String strVal(int doc) {
				// the string value of the ordinal, not the string itself
				return Integer.toString((end - arr[doc]));
			}

			@Override
			public String toString(int doc) {
				return description() + '=' + strVal(doc);
			}
		};
	}

	@Override
	public boolean equals(Object o) {
		if (o.getClass() != ReverseOrdFieldSource.class)
			return false;
		ReverseOrdFieldSource other = (ReverseOrdFieldSource) o;
		return this.field.equals(other.field);
	}

	private static final int hcode = ReverseOrdFieldSource.class.hashCode();

	@Override
	public int hashCode() {
		return hcode + field.hashCode();
	};

}
